1. Field Of The Invention
The present invention relates to acetabular prosthetic devices and more particularly to an improved acetabular prosthesis (and method of surgically implanting), wherein the prosthesis has a cup or shell that includes radially extending bores therethrough that can be used as drill guides by a surgeon after the acetabular cup or shell has been placed in the patient's acetabulum. Holes can be drilled surgically into the underlying bone tissue using the drill guide openings so that one or more pegs for improved anchoring can be placed into the bores and affixed rigidly to the acetabular cup using an interference or wedge fit. The prosthesis (including cup or shell and rigidly affixed pegs) is thus anchored into the underlying surgical openings. The cup has a shiny polished inner, concave surface that faces the liner so that relative motion between the liner and shell will generate minimal liner debris. The polished shell concave surface has a roughness of less that sixteen micro inches.
2. General Background
There are a number of commercially available acetabular prosthetic devices that include a cup shaped body, some of which have projections extending from the outer surface of the cup-shaped body. For example, U.S. Pat. No. 3,939,497 describes a socket for a hip joint prosthesis which is secured to a cavity in the bone tissue by a series of radially arranged pegs which can be projected outwardly from the wall of the socket into the surrounding tissue by a central screw which also has a self-tapping thread that enters the tissue.
U.S. Pat. No. 4,685,923 provides a hip joint socket made from a plastics material that can be installed without the use of bone cement or adhesive. The socket comprises a hemisphere of polyethylene. The socket may have four bores extending skewed to the equatorial plane to permit the surgeon to fix the socket in the acetabulum by means of screws or dowels temporarily or permanently. The primary anchoring is provided by two plugs or pins arranged on the outer surface of a socket. The pins may be substantially parallel to each other. The pins are inserted in bore holes drilled into the bone. The bore holes are drilled so that the pins are inserted under stress. A secondary anchor in the form of flaps are present near the actuarial plane of the socket. These flaps supplement the anchoring affect of the pins.
In U.S. Pat. No. 4,792,337 an acetabular cup is provided which has a metallic anchoring shell. The cup is for cement-less fixation in the acetabulum. The shell has several holes through which screws are driven into the bone. The screws have rounded heads and the holes are countersunk so that the orientation of the screws may be varied with respect to the cup and each other.
In U.S. Pat. No. 4,828,565 there is provided a cotyliodal component for a non-cemented hip prosthesis. The component has two parts, a titanium hemispherical shell and a cup of polymer which is engaged into it. The shell has two zones, the first zone is covered with porous titanium capable of being invaded by spongy bone and also has two projecting pieces. The other zone has a smooth metal surface. Two screws pass through the projecting pieces and are used to anchor the component in the acetabulum.
Another acetabular cup for cement-less fixation in the acetabulum is described in European Patent Application No. 13,863, published Jun. 8, 1980. The cup is anchored to the bone by a central pin and a number of other pins distributed over the surface of the cup. The pins have several sawtooth notches along their length. The bone may be pre-drilled to take the pins.
European Patent Application No. 169,978 published May 2, 1986, describes an acetabular cup which has an outer shell embedded into the patient's pelvis. The outer shell has a frustro-conical skirt and a spherical central cap. The shell has a number of small tufts with rounded ends projecting from its surface. The tufts are embedded in the bone tissue to provide improved anchorage.
In European Patent Application No. 211,169 published Feb. 25, 1987, an acetabular cup is described in which an external boss protrudes from the outer surface of the acetabulum body to fit into a pre-drilled hole in the acetabulum. The cup also has two anchoring lugs in the meridian plane. The lugs take screws to aid in anchoring the cup.
Other foreign patents and patent applications which describe acetabular cups include European Patent Application No. 212,087 published Apr. 3, 1987, wherein metallic pins project from the surface of the cup and contain holes in which tissue may grow. In European Patent No. 341,198 published Nov. 8, 1989, an acetabular cup has a metal outer shell and a plastic body for retaining the hip joint head. The shell is frustro-conical in cross-section with an opening at an apex and circular teeth around the outside. Three or more anchoring dowels parallel to the convexes protrude from the outer surface of the shells. The dowels are slotted and provide with circular teeth of a sawtooth cross-section over the portions which protrude. A central bolt may be fitted into the dowel to provide a rounded end.
The use of cement for fixation of acetabular process, and in some cases the use of spacers, is found in U.S. Pat. Nos. 4,563,778, and 4,566,138. This concept of the use of bone cement and spacers is also seen in United Kingdom Patent Nos. 1,170,295 and 2,080,118.
U.S. Pat. No. 4,923,473, issued to Peter Griss et al., entitled "Hemispherical Acetabulum", relates to a hemispherical acetabulum having a fixing pin which projects from the outside surface of the acetabulum.
In prior art acetabular cup prosthetic devices, the projections or spacers are often for the sole purpose of providing a space from the bone tissue that can be occupied by bone cement. Further, many acetabular cup prosthetic devices carry projections on their outer surface which are a part of the prosthesis as constructed and which cannot be added thereafter such as during surgery.
Still other prosthetic devices in the form of acetabular cups provide pegs which must be affixed to the tissue before the acetabular cup is placed in the position. Pegs which are preattached to the cup may require predrilling or other preparation which includes impaction for the purpose of forcing the projections into the bone. The bone bed may require advance preparation in some devices to accept the protrusions.